Figure 1125

Posterior view of exposed spinal cord. Note that each spinal nerve emerges from the cord by a number of dorsal (posterior) and ventral (anterior) roots. Note the dura mater (the outer layer of the meninges) and the denticulate ligaments of the pia mater, which anchor the spinal cord to the wall of the spinal canal. (From Barr ML, Kiernan JA. The Human Nervous System. New York: Harper a Row, 198b.)

called nuclei. In this context, the term nucleus means a cluster or group of neuronal cell bodies plus fibers and neuroglia. Nuclei of the CNS are the morphologic and functional equivalents of the ganglia of the PNS. Synapses occur only in the gray matter.

The cell bodies of motor neurons that innervate striated muscle are located in the ventral (anterior) horn of the gray matter

Ventral motor neurons, also called anterior horn cells, are large basophilic cells and are easily recognized in routine histologic preparations (Fig. 11.26). Because the motor neuron conducts impulses away from the CNS, it is called an efferent neuron.

The axon of a motor neuron leaves the spinal cord, passes through the ventral (anterior) root, becomes a component of the spinal nerve of that segment, and, as such, is conveyed to the muscle. The axon is myelinated except at its origin and termination. Near the muscle cell, the axon divides into numerous terminal branches that form neuromuscular synapses with the muscle cell (see page 257).

The cell bodies of sensory neurons are located in ganglia that lie on the dorsal root of the spinal nerve

Sensory neurons in the dorsal root ganglia are pseudo-unipolar. They have a single process that divides into a pe-